1. Field of the Invention
The present invention generally relates to semiconductor devices and semiconductor device modules, and more particularly to a semiconductor device and a semiconductor memory module which can suitably be used as a high-speed performance memory and a high-speed performance memory module, respectively.
A graphic process executed in office automation devices such as a personal computer and a workstation has been required to process a huge amount of information in a short time. Hence, there has been considerable activity in speeding up a semiconductor memory device and increasing the storage capacity. Also, the semiconductor memory device has been required to operate at a higher frequency and have a package structure suitable for high-frequency operation.
2. Description of the Related Art
Generally, the capacity of the memories built in the office automation devices is attempted by adding a new semiconductor memory device module thereto or replacing the old module by new one. Usually, such a semiconductor memory device module is called a SIMM (Single Inline Memory Module), which has a circuit board on which semiconductor memory devices such as DRAM devices are mounted. Terminals are provided along one end of the circuit board. The module can be detachably attached to a socket provided in the office automation devices.
The semiconductor memory devices are designed to terminals (leads) for external connection as short as possible in order to make it possible to operate the devices at a higher speed. For example, the following package structures are known: LCC (Leadless Chip Carrier), QFN (Quad Flat Non-leaded package), QFJ (Quad Flat J-leaded package), and SOJ (Small Outline J-leaded package).
The LCC and QFN have a high-speed-oriented package structure in which no leads are provided but electrode pads for soldering are provided to a resin package. The QFJ and SOJ have another high-speed-oriented package structure having J-shaped leads extending from a resin package in order to shorten the leads.
However, the semiconductor devices having the above-mentioned package structures have the following disadvantages. The leads and electrode pads (hereinafter referred to as lead members generally) are not connected directly to a semiconductor chip but are connected by using wires. Hence, in a state in which the semiconductor devices are mounted on a circuit board, the lead members and the wires exist in the electrical transmission lines between the semiconductor chips and the connecting points on the circuit board. Thus, the electrical transmission lines have a large electrical resistance (impedance).
The semiconductor chip is completely buried in the resin package, so that there is a long distance between the semiconductor chip and the outer circumference of the resin package (that is, the positions of the lead members). This arrangement also increases the electrical resistance.
When the semiconductor device having any of the above-mentioned structures is operated in synchronism with a clock signal having a very high frequency, the electrical transmission lines have a large loss, so that a desired processing speed cannot be realized.
One may consider increasing the area of the lead members and the diameter of the wires in order to reduce the electrical resistance. However, such an increase increases the size of the semiconductor devices and does not satisfy down-sizing and thinning demanded by the users.